Azimuth adaptive phased array sonar

Abstract

In ultrasonic transmission from and reception by an array probe in a phased array sonar, when an ultrasonic beam is directed substantially in front of the array probe, an ultrasonic wave having a high center frequency f o , or a bandwidth extending into higher frequencies, is transmitted and/or received in order to insure a high image resolution. When the ultrasonic beam is steered sideways, an ultrasonic wave having a lower center frequency f o , or a higher frequency range cutoff in relation to a steering angle θ, is transmitted and/or received in order to increase the angle at which grating lobes are generated and hence prevent such grating lobes from entering the angle range of the field of view.

What is claimed is: 
     
       1. An azimuth adaptive phased array sonar (see FIG. 3), comprising a sensor (4) having an array of a plurality of ultrasonic transducer elements (4) which transmit ultrasonic signals and receive echo signals;   a first delay stage (2a) which in accordance with a trigger signal supplied from a trigger generator (2) generates a plurality of driving signals having a phase relationship corresponding to the direction of transmission of the ultrasonic beams, respectively;   a pulser (3) for amplifying the driving signals to produce output signals which drive said individual ultrasonic elements (4);   an amplifier (5) for amplifying the echo signals detected by said individual ultrasonic transducer elements (4), respectively;   a second delay stage (2b) for delaying the respective output signals of said amplifier (5) for achieving a phase relationship corresponding to the direction of reception of the echo signal;   control means (7) for controlling the phase relationship in said first delay stage (2a) and said second delay stage (2b) in accordance with the respective direction of transmission of the ultrasonic signals and directions of reception of the echo signals;   a bandpass filter (6) disposed in a signal path of received echo signals and/or in a signal path of producing ultrasonic signals, said bandpass filter (6) having a variable frequency response; and   wherein said control means (7) further controls said bandpass filter (6) so as to substantially shift the pass band toward a lower frequency side as the azimuth of the ultrasonic beam is increased.   
     
     
       2. The sonar of claim 1, wherein said bandpass filter (6) is controlled by said control means (7) to lower a central frequency as the azimuth of the ultrasonic beam is increased. 
     
     
       3. The sonar of claim 1, wherein said bandpass filter (6) is controlled by said control means (7) to narrow said pass bandwidth as the azimuth of the ultrasonic beam is increased. 
     
     
       4. The sonar of claim 1, wherein said bandpass filter (6) is controlled by said control means (7) to lower both higher cutoff frequency and lower cutoff frequency as the azimuth of the ultrasonic beam is increased. 
     
     
       5. The sonar of claim 1, wherein said bandpass filter (6) is controlled by said control means (7) to process a signal indicative of the received ultrasonic beam immediately subsequent to generation of a composite received ultrasonic beam. 
     
     
       6. The sonar of claim 1, wherein said bandpass filter (6) is controlled by said control means (7) to process all signals indicative of received ultrasonic beam from said transducer elements (4) involved in reception of the ultrasonic beam. 
     
     
       7. The sonar of claim 1, wherein said bandpass filter (6) is controlled by said control means (7) to process each output from a pulser (3) which generates pulses for energizing said array probe. 
     
     
       8. The sonar of claim 1, wherein said bandpass filter (6) is controlled by said control means (7) to process an original transmission signal to be delayed for energizing said array probe (4).